The ubiquitous random access memory enables direct read or write access to data at an arbitrarily specified address, but allows only one address to be accessed at a time. Writing test patterns in such a memory is a lengthy process, because it is necessary to write to every address individually. Long test times add to the manufacturing cost of the memory.
Random access memories are generally initialized by a software routine that writes initial data at each address successively, but this also takes time. The result is the annoying delay experienced, for example, when a personal computer is switched on.